Hello, I am a friend of Thrawn's...
Thrawn has been getting a fair amount of his LOTR trivia from me, while I was at work, so I apologize for any inaccuracies of specific details. I do believe that while it was more than 3000 years since the creation of Numenor (and fall, and the move of Isildur and his father back to the old world) to present "Fellowship of the Ring" days, I do know that the line of Numenorian kings were VERY long lived. They kept the blood line pure...
The first king reigned for about 800 years?? Even Aragorn, who was pretty far down the line, reigned for three hundred years after the "Return of the King". This demonstrates that although there has been many, many years since the start of the half breed line, since they were so long lived, there aren't as many generations between them as you may think.
To me, that would demonstrate more than a tiny smattering of elvish blood...